1. Field of the Invention
The present invention relates to sensor magnet mounting devices and particularly to a sensor magnet mounting device for mounting a sensor magnet to be used for detection of a running speed of a two-wheeled vehicle.
2. Description of the Background Art
These days, a speed meter is often mounted on a bicycle to make it easy for the user to have information about the running speed, running distance etc. of the bicycle.
FIG. 8 is an appearance view of a bicycle in which a general display device is incorporated in a speed meter; FIG. 9 is an enlarged view of the portion "X" in FIG. 8; FIG. 10 is a plan view of the receiver shown in FIG. 8; and FIG. 11 is an enlarged perspective view of the mounting portion of the sensor magnet shown in FIG. 9.
Referring to those figures, the structure will be described.
A conventional sensor magnet mounting device includes a signal generating portion and a transmitting portion which are formed by a transmitter 28 detachably mounted on a fork 34 of a front wheel of a bicycle 24, and a sensor magnet 10 detachably mounted on spokes 32 of the front wheel. The sensor magnet 10 is located at a distance from an axle 36 of the front wheel corresponding to the distance (B) between the axle 36 and the transmitter 28.
Thus, each time the sensor magnet 10 passes by the transmitter 28, a contact of a switch (not shown) incorporated in the transmitter 28 is closed by the function of the magnet to generate a signal. The generated signal is transmitted from the transmitter 28 to a receiver 30. The receiver 30 evaluates various data such as the running speed or running distance of the bicycle by counting the transmitted signal. The receiver 30 includes a display portion 16 of liquid crystal, for example, for displaying results of evaluation as required, and a selection switch 38 for arbitrary selection of a display of any of the results of evaluation etc.
The sensor magnet 10 is disposed between two spokes 32 as shown in FIG. 11. A magnet portion 12 is fixed to the two spokes 32 by tightening of set screws 15 in mounting holes 14 of the magnet portion 12 opposite to a mounting plate 13 with the two spokes 32 put therebetween.
In the above-described conventional sensor magnet mounting device, the sensor magnet is mounted on the spokes only by means of the set screws and the mounting is liable to be loosened due to vibrations caused by the running.
The distance between the two spokes where the mounting is made increases according to increase in the distance from the center of the axle of the wheel and in order to accurately detect passage of the sensor magnet by the sensor, it is preferable to mount the sensor magnet in a position distant from the axle. This is because it is easier to detect whether or not the sensor magnet passes by the sensor, as the circumference of rotation of the sensor magnet becomes longer.
The mounting position of the sensor magnet distant from the center of the axle signifies that the mounting position of the transmitter approaches the receiver, which is preferable for operation of transmitting and receiving signals.
However, if the distance B shown in FIG. 9 is increased, the spacing of the spokes becomes large and it is necessary to increase the length of the magnet portion, which involves disadvantages in mounting stability and costs.